(1) Field of the Invention
The invention relates to an organic light emitting diode (OLED) display, and a method of making same. More particularly, this invention relates to an OLED structure including an insulating layer which functions to control the light emission region of each pixel thereby improving the uniformity of image manifestation.
(2) Description of the Prior Art
Owing to high brightness, fast response speed, light weight, thin and small features, full color, no viewing angle differences, no need for an LCD back-light board and low electrical consumption, an organic light emitting diode display or organic electroluminescence display (OLED) takes the lead to substitute a twist nematic (TN) or a super twist nematic (STN) liquid crystal display. Further, it substitutes for a small-sized thin-film transistor (TFT) LCD to become a new display material of fabricating portable information products, cell phones, personal digital assistant (PDA) and notebook.
Conventional OLED display structures are built on glass substrate in a manner such that a two-dimensional OLED array for image manifestation is formed. Each OLED in the array, referring to FIG. 1, generally includes overlaying layers starting with a light transmissive first electrode 12 formed on the substrate, an organic electroluminescent (EL) emission medium 10 deposited over the first electrode 12, and a metallic electrode 14 on top of the organic electroluminescent emission medium 10. When an electrical potential is placed across the electrodes, holes and electrons are injected into the organic zones from the anode and cathode, respectively. Light emission results from hole-electron recombination within the device.
As shown in FIG. 2, conventionally, the first step for manufacturing OLED display is to evaporate or sputter light transmissive first electrodes 102 (e.g. of indium-tin-oxide or ITO) on a glass substrate 100. Then an emission layer 116 (e.g. of organic electroluminescent medium) is evaporated on the electrode 102 by using a shadow mask 112 which has been defined holes thereon. This is because all the holes have same size “T” that all the emission layer blocks have same size. However, the realistic condition is the shadow mask 112 may droop causing of temperature, weight, etc. Then each hole may not have same size (e.g. T1′{grave over ( )}T2′{grave over ( )}T3′ as shown in FIG. 2) that the emission layer blocks result to different size. Consequently, each pixel of light emission region is changed and result in a problem of non-uniformity and bad quality of image manifestation. Thus, to solve the above-mentioned problem is the most important issue nowadays.
It is a purpose of this invention to fulfill the above described needs in the art, as well as other needs which will become apparent to the skilled artisan from the following detailed description of this invention.